This invention relates to a flywheel magneto generator and more particularly to a flywheel magneto generator used for an internal combustion engine.
There has been widely used as a generator for an internal combustion engine a flywheel magneto generator having an ignition unit provided on a side of a stator. Such a magneto generator is constructed as shown in FIGS. 3 and 4. The front face of the prior art flywheel magneto generator is shown in FIG. 3 and a cross section taken along the line IVxe2x80x94IV of FIG. 3 is shown in FIG. 4.
In these figures, a flywheel 1 is mounted on a rotational shaft of an internal combustion engine not shown and rotationally driven by the internal combustion engine. A permanent magnet 2 is provided in a groove in a peripheral wall 1a of the flywheel 1. A plurality of blower blades 1c are formed on an outer face of a bottom wall portion 1b of the flywheel 1 so as to stand in a line along the peripheral wall portion 1a. A boss 1e is formed at a central portion of the bottom wall portion 1b of the flywheel and mounted on the not shown rotational shaft of the internal combustion engine.
A stator core 5 is mounted on a member secured to an engine case or the like and has a pair of magnetic pole portions 5a and 5b disposed in a spaced manner in a peripheral direction of the flywheel 1 so that the magnetic pole portions 5a and 5b are faced to the outer face of the peripheral wall portion 1a of the flywheel 1 and to the permanent magnet 2.
An ignition unit 6 is mounted on the stator core 5. The ignition unit 6 comprises an ignition coil 6a having a primary coil 6a1 and a secondary coil 6a2, electronic devices (not shown) forming a part of an ignition system for the internal combustion engine together with the ignition coil 6 and a cover portion 6c to cover the ignition coil 6a and the electronic devices. The cover portion 6c is formed of a conventional insulating resin mold layer.
Of late, since the control of the ignition timing gets complicated because of attaining a purification of an exhaust gas and aiming at saving of a fuel cost, in many cases, a digital control system having a microcomputer used therein has been used as the ignition unit 6. Thus, in many cases, the electronic devices disposed within the cover of the ignition unit 6 include the microcomputer weak to heat as well as switch elements for controlling the primary current of the ignition coil.
Since, in this ignition unit, heat is generated from the ignition coil 6a and the electronic devices such as the switch elements for controlling the primary current of the ignition coil, a temperature of the ignition unit rises. Thus, in order to protect the electronic devices, the ignition unit 6 should be cooled and to this end, the blower blades 1c, 1c, - - - are provided on the bottom wall portion of the flywheel.
In the magneto generator of FIGS. 3 and 4, there is generated a flow of cooling wind sent out outwardly in the diametrical direction of the flywheel 1 by the blower blades 1c, 1c, - - - when the flywheel 1 rotates in a direction indicated by an arrow of FIG. 3 with the rotation of the engine. This cooling wind flows outwardly in the diametrical direction along the outer face of the bottom wall portion as indicated by an arrow Wxe2x80x2 of FIG. 4, the most of the cooling wind flows while going past by the ignition unit 6 without contacting it directly. Thus, there arises a problem that it is hard to cool the ignition unit 6 effectively.
Especially, in the case where the electronic devices forming the ignition unit 6 include the microcomputer weak to heat, it is required that the temperature of the ignition unit is maintained at a value equal to or less than a limit value in comparison with the prior art ignition unit, but it is hard that the prior art flywheel magneto generator complies with such a request.
Accordingly, it is a principal object of the invention to provide a flywheel magneto generator adapted to improve a cooling effect of an ignition unit by increasing the amount of a cooling wind contacting the ignition unit.
A magneto generator of the present invention comprises a cup-shaped flywheel having a peripheral wall portion and a bottom wall portion and mounted on a rotational shaft of an internal combustion engine and driven by the internal combustion engine with a plurality of blower blades provided on an outer face of the bottom wall portion so as to be arranged along the peripheral wall portion, a permanent magnet provided in a groove in an outer face side of the peripheral wall portion of the flywheel, a stator core having magnetic pole portions disposed in a spaced manner in the peripheral direction of the flywheel so that the magnetic pole portions are faced to the peripheral outer face of the flywheel and the permanent magnet and an ignition unit secured to the stator core and having and ignition coil wound on the stator core, electronic devices forming at least a part of an ignition system for the internal combustion engine together with the ignition coil and a cover portion to cover the ignition coil and the electronic devices. In the invention, the flywheel comprises at least one recess provided on the bottom wall portion thereof an outer face of the peripheral wall of the flywheel.
With the recess provided in the bottom wall portion of the flywheel opening between the adjacent blower blades and extending to the outer face of the peripheral wall portion of the flywheel, respectively as aforementioned, the inside of the recess gets a negative pressure when the flywheel rotates. Thus, the flow of the cooling wind generated by the blower blades is drawn in the recess. The thus drawn cooling wind is drawn closer to the bottom portion of the recess (to the central part of the ignition unit) and sent out toward the ignition unit by means of centrifugal force generated with the rotation of the flywheel whereby the amount of the wind blown directly against the ignition unit increases. Thus, the ignition unit can be effectively cooled and therefore in the case where the temperature of the ignition unit should be reduced to the lower value such as the case where the microcomputer is provided in the ignition unit, the generator can comply with such a request.
The recess may be preferably provided so that the diametrical direction opening is faced to at least a part of the magnetic pole portions of the stator core.
With the recess provided in this manner, the amount of the cooling wind blown directly against the stator core increases and therefore cooling of the stator core is promoted. This increases the difference of the temperature between the ignition unit and the stator core. Thus, the heat conduction from the ignition unit to the stator core can be made better and cooling of the ignition unit can be more effectively made on the synergistic effect of the heat exchange performed between the outer surface of the ignition unit and the cooling wind and the heat dissipation performed through the stator core from the ignition unit.